The invention is applicable especially to apparatus with a hyperstoichiometric premix burner, that is wherein air is admixed to the gas inside the burner in larger amounts than the required amount for stoichiometric combustion.
An apparatus with an atmospheric burner is described in Italian Patent Application No. MI92A002510 filed on Nov. 2, 1992 by this Applicant. The apparatus comprises, additionally to the atmospheric burner, a combustion chamber and means for creating a vacuum within the combustion chamber relatively to the nozzle area. The burner has gas outflow nozzles, suction and mixing ducts coaxial with the nozzles, and diffusers communicated to the ducts for delivering the gas/primary air mixture into the combustion chamber. The apparatus further comprises a box-type structure connected to the combustion chamber and enveloping the suction and mixing ducts. That structure has a wall laid across between the nozzles and the ducts, and for each nozzle, an intake opening wherethrough primary air is drawn into the ducts and secondary air intake openings adjacent to the primary air intake opening. The streams of primary air and secondary air through their respective openings flow along parallel directions to each other.
The apparatus just outlined provides for uniform and complete combustion of the gas using extremely simple constructional expedients. However, it may still develop ignition problems, i.e. at the start of its operation, and where instead of the standard gas for which the apparatus is set, a gas prone on flame separation from the same family as said standard gas or a so-called "poor-combustion" gas or a so-called "backfiring" gas from the same family are used. Specifically, the diffuser temperature may occasionally attain a critical danger value, and on some other occasions, the flame may become unstable, resulting in poor combustion of the fuel gas. Such problems are felt the more heavily when the premixing of air to the gas is raised above that required for stoichiometric combustion in order to cut down harmful emissions.